1. Field of the Invention
This invention relates to an excavator such as a backhoe, and more particularly to a piping structure for supplying and draining pressure oil to/from a boom cylinder, an arm cylinder and a bucket cylinder.
2. Description of the Related Art
An excavator such as a backhoe has an excavating implement attached to the front of a swivel base (vehicle body). The excavating implement includes a boom movable up and down by a boom cylinder, an arm pivotally attached to a distal end of the boom to be swingable by an arm cylinder, and a bucket pivotally attached to a distal end of the arm to be swingable by a bucket cylinder to take dumping and scooping action. These cylinders are connected to control valves arranged on the swivel base, through a group of flexible hoses, to supply and drain pressure oil to/from the cylinders.
This excavating implement has the boom movable up and down, the swingable arm, and the bucket taking dumping and scooping action. To operate (i.e. drive) these components, the cylinders are connected through flexible hydraulic hoses to control valves arranged on the swivel base (vehicle body).
The hydraulic hoses have lengths thereof to the control valves variable from a lowermost position to an uppermost position of the boom. Such variations in hose length are accommodated by the flexibility and intermediate slacks of the hoses. Conventionally, however, the above slacks, i.e. curves for absorbing differences in hose length, are formed adjacent a bottom portion of the boom. When the boom moves up and down, the curves undergo changes in size. When the boom moves up, the curves protrude to a large extent toward the swivel base (vehicle body). This impairs operability and particularly visibility during an excavating operation. In order to dig a ditch or the like, the boom is pivotally attached to a swing bracket swingable right and left, to be vertically movable (up and down). Thus, the boom is movable up and down and right and left, and the flexible hydraulic hoses must follow such movements. This tends to cause twisting of the hoses, thereby impairing durability of the hoses.
As a conventional example, a small backhoe is described in Japanese Patent Laying-Open Publication H9-60039. This backhoe includes a swivel body mounted on a traveling device to be rotatable about a vertical axis, and an excavating implement. The latter has a boom pivotally attached to the swivel body to be swingable about a horizontal pivot, an arm pivotally attached to a distal end of the boom, and a bucket attached to a distal end of the arm for scooping and dumping action. A control valve unit is mounted in the swivel body for supplying pressure oil to various actuators to drive the excavating implement and the traveling device in the form of caterpillar tracks.
Since the boom of the excavating implement is vertically swingable about the pivot, flexible hydraulic hoses are employed as hydraulic piping for supplying pressure oil to the hydraulic cylinders disposed on the boom. The hydraulic hoses are arranged to have allowances in length adjacent the pivotal connection of the boom. In arranging the hydraulic hoses are arranged to have allowances in length adjacent the pivotal connection of the boom, the above conventional backhoe passes the flexible hydraulic hoses through an area far rearwardly (close to the swivel body) of the pivot of the boom (see FIG. 6 of Patent Laying-Open Publication H9-60039). Consequently, when the boom is raised to its uppermost position, the hydraulic hoses bulge to a large extent rearward. The bulging hydraulic hoses impose corresponding restrictions on an operator-accommodating space on the swivel body. The bulging hydraulic hoses also present an obstruction to impair operability.
The conventional boom (boom structure) has a forked proximal end extending a main boom body and having a collar or bush mounted in between. The swing bracket has a forked portion that sandwiches the forked end of the boom, with a horizontal pivot extending through the bush for pivotally attaching the boom to be movable up and down. This construction requires the forked proximal end of the long, large boom structure to be machined. Such a machining process is troublesome and with low machining accuracy.
To solve such a problem, Japanese Patent Laying-Open Publication No. 2000-96610 proposes the following excavators. One is an excavator having a swing bracket pivotally attached to a swivel base to be swingable about a vertical axis, and a boom structure with a proximal end thereof attached to the swing bracket to be movable up and down about a horizontal pivot, characterized in that the swing bracket is pivotally attached through the horizontal pivot to the swing bracket sandwiched by the proximal end, a space surrounded by the proximal end being formed forwardly of the pivot, a group of hoses for pressure oil having passed the swing bracket passing upward through that space.
Another is an excavator having a swing bracket pivotally attached to a swivel base to be swingable about a vertical axis, and a boom structure with a proximal end thereof attached to the swing bracket to be movable up and down about a horizontal pivot, characterized in that the swing bracket as sandwiched by the swing bracket is pivotally attached through the horizontal pivot to the swing bracket, a space surrounded by the proximal end being formed forwardly of the pivot, a group of hoses for pressure oil having passed the swing bracket passing upward through that space.
These prior constructions (proposed techniques) overcome various disadvantages caused by bulging of the group of hoses occurring with vertical movements of the boom. However, such bulging cannot be avoided entirely since the group of hoses is not guided in the space. Where the above space is enlarged by elongating the proximal end in order to prevent the bulging entirely, an excessive moment will act on the pivot. This results in a concentration of stress and a lower excavating performance.
An object of this invention is to provide a swivel working vehicle overcoming the above inconveniences. Specifically, the invention intends to provide a swivel working vehicle including a swivel base having a curved length absorbing portion for absorbing differences in hose length occurring with vertical movements of a boom, to realize excellent visibility, and hence operability, and significantly improve the durability of hoses.
Another object of this invention is to provide an excavator and a boom structure which achieve excellent visibility to improve excavating performance significantly by retaining the advantage of the above proposed technique and with a simple technique of forming a hose guide surface in a forked proximal end.
The above objects are fulfilled, according to this invention, by an excavator comprising:
a traveling device;
an excavating implement including a boom movable up and down by a boom cylinder, an arm pivotally attached to a top end of the boom to be swingable by an arm cylinder, and a bucket pivotally attached to a top end of the arm to be driven by a bucket cylinder for scooping and dumping action;
a swivel base supported by the running device and supporting the excavating implement, the swivel base having control valves for supplying and draining pressure oil to/from the cylinders, respectively; and
a group of flexible hoses connected between the control valves and the cylinders for transmitting the pressure oil therebetween, the group of flexible hoses having a length absorbing portion disposed in the swivel base for absorbing variations in hose length occurring with vertical movement of the boom.
As noted above, this invention employs a construction in which a curved length absorbing portion is disposed in the swivel base, rather than on the boom, for absorbing variations in hose length occurring with vertical movement of the boom. Thus, when an excavating operation is performed by moving the boom up and down and swinging the arm, the group of flexible hoses does not bulge to obstruct view. Moreover, the operator need not concern the hoses contacting the swivel base (swivel body) and can therefore move the boom up and down quickly to improve operability.
In addition to the above construction, the swivel base may have a swing bracket pivotally attached thereto for swinging the excavating implement about a vertical axis, the boom may have a forked portion connected to the swing bracket, and the forked portion may define a guide surface inclined downward toward the swing bracket to guide the group of flexible hoses in a space surrounded by the forked portion. Since the group of hoses is guided along the inclined surface, the hoses are reliably prevented from lifting (bulging) from the boom.
It is also preferred that the forked portion has a clamp for holding the group of flexible hoses extending through the space to follow the guide surface.
The group of flexible hoses may extend fore and aft through the swing bracket. Then, the group of flexible hoses moves fore and aft with vertical movement of the boom to absorb variations in hose length. This allows a diminishment of the degree of curvature of the length absorbing portion disposed in the swivel, to reduce the chance of its interference with various equipment disposed in the swivel base. The length absorbing portion does not undergo complex up and down and right and left movements, thereby avoiding twisting of the hoses.
By forming the length absorbing portion in the swivel base, its curving or bulging direction may be upward or horizontal, which may be determined by taking various equipment in the swivel base into account. Thus, the hoses may be arranged with an increased degree of freedom.
Further, it is recommended that the group of flexible hoses includes a first group of hoses extending through the swing bracket to the boom cylinder, and a second group of hoses connected to the arm cylinder and the bucket cylinder, and that the second group of hoses is passed upward through a space formed in a bottom portion of the boom.
With this construction, the group of hoses (first group of hoses) for the boom cylinder does not protrude from the bottom portion of the boom. This group of hoses and the group of working hoses (second group of hoses for the bucket and arm) are separated to facilitate maintenance of the group of working hoses.
The group of hoses may further include a third group of hoses connected to a service port, the first, second and third groups of hoses being arranged parallel to one another on a surface of the boom and connected to steel pipes through a relay unit.
With this construction, the group of working hoses (second and third groups of hoses) are arranged parallel within a width of the boom to extend longitudinally of the boom. Thus, the hoses are not obstructive to view, and have a reduced chance of interference with other objects.
These and other features, functions, effects and advantages of the present invention will be appreciated upon reading the following description with reference to the drawings.